To clarify influences induced by non-uniform ground surface on I.G.E. hover
performance of a rotor, a numerical prediction method is developed by comb
ining a foe-wake method with a panel method, where the most important featu
re is the ability to determine blade flapping motions to be consistent with
the deformed wake geometry. The ground surface beneath the rotor is substi
tuted for quadratic panels with unknown ground vortex strength which are de
termined by virtue of the non-penetration conditions at the collocation poi
nts. The rotor blades are modeled by the lifting lines with a constant circ
ulation which results in a wake structure to compose of deformed helical li
ne vortices trailing from the blade tips. The numerical procedure is progra
mmed as an interactive two-stage process, where the spatial arrangements of
tip vortices are calculated at first by moving their nodal points with upd
ated local velocities induced by the ground and trailing vortices and then
proceed to the second stage where the equation of blade flapping motion is
served using averaged induced velocity distribution on the rotor disc. Iter
ations are executed until both the wake geometry and blade flapping motions
are converged simultaneously. In this paper, we introduce typical numerica
l results obtained for a rotor hovering in close proximity above a uniforml
y inclined flat surface and discuss influences of the ground inclination an
gle and rotor height on the wake geometry, flowfields around the rotor and
the rotor-induced torque. The ground interaction effect on the amplitude an
d phase angle of the blade flapping motion are also investigated, and their
unique dependencies on the operating circumstances are clarified.